An overvoltage protection device comprising a thermal disconnection device is already known from the German Utility Model DE 295 19 313 U1. The surge arrester described in this document comprises a lower part which is electrically connected to ingoing and outgoing leads of the system to be protected or the device to be protected. In addition, a plug-in part is provided, which comprises at least one varistor. The plug-in part can be detachably, yet electrically connected to the lower part by a mechanical connector. A thermal release is provided on the plug-in part in the event of the varistor being inadmissibly heated. A supporting wall is located in the plug-in part, with the varistor being mounted on a side face of the supporting wall and the thermal disconnection device as well as corresponding connection means being provided on the other side face of the supporting wall. Thus, the thermal release is placed opposite the varistor.
The prior plug-in part is trough-shaped, with the bottom of the trough forming the aforementioned supporting wall and the edge of the trough surrounding the region next to the supporting wall in which the varistor provided on the supporting wall is located. The varistor itself is provided with two connecting lugs serving the electrical connection. One of the connecting lugs is connected to the thermal release element.
In the overvoltage protection device according to EP 0 727 091 B1 two or more varistors accommodated in a housing are provided as protection elements, whose earth electrodes are electrically interconnected by means of a strip with a contact piece. The mains electrodes are connected to contact pieces by means of disconnection devices connected in series to the protection elements.
According to EP 0 727 091 B1 the problem is to be overcome to simplify the disconnection device in structure, without disadvantageously affecting the protective properties.
To this end, all disconnection devices are arranged in the pivoting region of the web of an essentially U-shaped bail designed as a rocker and swivel-mounted in the housing. A displaceably mounted actuating bolt is bearing on the web, and an indicating device is further arranged on the bail. As a common rocker is allocated to all the disconnection devices, in turn allocated to protective elements installed in the overvoltage protection device, the construction is simplified. All the same it is ensured that when the disconnection device is opened (released), i.e. also when only one disconnection device is opened, the actuating bolt is displaced and the provided release indicating device reaches a position which indicates that an exchange of the overvoltage protection device is necessary.
In the device for protection against the occurrence of transient electrical overvoltages according to EP 0 716 493 B1 at least two varistors are provided. Moreover, separating means are provided which are sensitive with respect to the condition of the varistors, especially in thermal terms. Each of the varistors can and should be disconnected separately.
The generic document WO 2007/105066 A1 describes an overvoltage protection device comprising two disc-shaped varistors and a gas arrester, with the varistors and the gas arrester being interconnected in a Y-arrangement.
The varistors and the gas arrester are located on a circuit board. The two connection pins of the varistors are oriented to face each other, and a metallic electrical bridge is provided interconnecting the aforementioned connection pins by means of low-melting solder.
The bridge is held under a preload by means of a spring, with the spring being supported with one spring end on a bolt fixed on the circuit board.
The disconnecting bridge is connected to the gas arrester by means of a conductor section. In one practical embodiment the conductor section is realized as a flexible strand.
If the varistors are thermally overloaded the melting temperature of the low-melting solder is reached and the bridge is moved away from the connection pins of the varistors in the disconnecting direction. This solution, too, just like the other prior art, requires an additional separating means. Moreover, there is the risk of an undesired one-sided separation of the bridge.